The invention relates to an arrangement and a method for performing positioning. In particular, the invention relates to determining the location of desired devices three-dimensionally.
How to determine the location of various mobile objects is a field under research. Various positioning methods have been developed for different mobile objects. One known solution is satellite positioning. It is based on the idea that orbital satellites transmit detectable and distinguishable signals at known frequencies. When a particular satellite receiver receives a signal from a plurality of satellites, it is able to determine its own location by means of signal transit time delays. One of these satellite positioning methods is known as Global Positioning System (GPS).
Various radio systems utilize system-specific characteristics in positioning. One positioning method known in cellular radio systems is based on the times of arrival (TOA, Time of Arrival; TDOA, Time Difference of Arrival) of the signals. In general, this method employs an extra receiver placed in connection with the radio system base stations, which receiver listens to mobile station transmission intended for another base station that serves the mobile station. The capacity of the method is limited, because each extra receiver can reliably measure only one mobile station at a time. Another method known in the cellular radio systems is based on the observed time difference (OTD) between the signals. In this method a mobile station measures the time difference between the base stations. The method requires information on the real time difference (RTD) of the base stations, if the base stations are not in synchronization. Positioning is performed on the basis of these data. These methods are only applicable in connection with the cellular radio systems.
One known method for radio transmitter positioning is a so-called direction finding (DF) method. In this method a signal transmitted by a mobile station is received by at least two DF receivers. Each DF receiver estimates the direction from which the mobile station signal is arriving. On the basis of this information it is possible to create a sector from each DF receiver, in the direction of which the mobile station is located. It can be determined that the mobile station is located at the intersection area of two or more sectors.
Drawbacks with the prior art solutions include inaccuracy and limited applicability. For instance, the methods based on the cellular radio systems are only applicable in the coverage areas of the systems, and they are not suitable for monitoring a large number of mobile stations, because the positioning would load the network excessively. Furthermore, most known methods perform positioning only two-dimensionally, and therefore they are not suitable for use inside buildings, for instance.
The object of the invention is to provide a method and an arrangement implementing the method, which allows accurate and three-dimensional positioning of desired mobile stations. This is achieved by a method for positioning one or more mobile stations, in which the location of the mobile stations is determined in the horizontal direction using at least two direction finding stations. The method of the invention comprises maintaining on a server information on the location of each mobile station; measuring in a mobile station at least one variable proportional to the location of the mobile station in the vertical direction; signalling information from the mobile station to a control unit on the measurement results time-divisionally at the same frequency controlled by the control unit; determining in the control unit the location of each mobile station in the vertical direction on the basis of the signalled data; and transmitting the data on the location to the server; determining the three-dimensional location of the mobile stations in the server; displaying the location of at least some of the mobile stations graphically.
The invention also relates to an arrangement for performing the positioning, comprising a set of mobile stations to be located and at least two direction finding stations for determining the location of the mobile stations.
In the arrangement of the invention, the mobile stations are arranged to measure at least one variable proportional to altitude; and the arrangement comprises a server, which maintains information on the location of each mobile station; a control unit, which controls over a radio path the mobile station transmissions such that the mobile stations signal data to the control unit on the variable proportional to the altitude time-divisionally at the same frequency, and which control unit is arranged to determine at which altitude the mobile station is located on the basis of the data signalled by the mobile station; and to signal the altitude information to the server and that the server is arranged to determine the three-dimensional location of the mobile stations on the basis of the radio direction finding measurement and the altitude information, and that the arrangement comprises workstations arranged to display the location of at least some of the mobile stations graphically.
Embodiments of the invention are described in the dependent claims.
In the solution of a preferred embodiment of the invention three-dimensional positioning of transceivers is based on the use of radio direction bearings and data transmitted by transceivers and measured by sensors. A plurality of transceivers can be located using only one frequency by means of time division technique. High accuracy and good radio signal propagation also inside buildings are achieved by using frequencies within VHF or UHF range.
Several advantages are achieved with the method and arrangement of the invention. The solution allows three-dimensional positioning of a large number of transmitters and monitoring of their locations using just one radio frequency. Thus, the solution is extremely spectrum-efficient. Further, the transmitter structure is simple, because they need not support a large number of frequencies.
Time division refers here to the fact that transmitters transmit at the same frequency but at different times. Time division can be implemented as a polling arrangement, for instance, in which a control unit controls each portable transceiver to transmit at a given time.
In some preferred embodiments DF stations carrying out two-dimensional positioning are movable, such as vehicle-mounted stations. This enables flexible use of the arrangement in various applications. For instance, in case of a fire, mobile DF stations can be placed in different quarters of the fire area and the firemen can be equipped with portable transceivers. The DF stations measure the location of the transceivers in the horizontal direction. The transceivers measure e.g. atmospheric pressure and signal the measurement results to the control center of the arrangement. The control center also measures the atmospheric pressure, and the transceiver measurement results are scaled such that the location of each transceiver is found out in the vertical direction. The solution thus allows monitoring the location and movements inside the building of each fireman equipped with the transmitter. The location can be displayed graphically on a workstation screen. If so desired, it is very easy to illustrate the location by displaying the graphic on a suitable map base. The altitude at which the transceivers are located can be illustrated by different colours, for instance.
In some embodiments the transmitters comprise various sensors, which may measure ambient conditions. For instance, measurements of gas concentration and temperature may give valuable information, by which the safety of the firemen can be ensured.
In some embodiments the transceivers can be divided into different groups and observation can be performed groupwise.
Advantageously the arrangement comprises a control unit, which communicates with portable transceivers time-divisionally and a server, which controls the operation of the whole arrangement.